The present inventive technology, in embodiments, includes enhancing light non-aqueous phase liquid (“LNAPL”) degradation to accelerate dense non-aqueous phase liquid (“DNAPL”) degradation; and perhaps even amending uric acid and uric acid-containing wastes as nitrogen sources in biodegradation of perhaps both LNAPL and DNAPL.
LNAPLs, including but not limited to gasoline, diesel, motor oil, and the like continue to be common contaminants in soils, groundwater, and the like. Bioremediation is an effective technique used in degrading LNAPL, which are converted into harmless by-products. Aerobic degradation dominates LNAPL remediation. In groundwater where oxygen is depleted, LNAPL can be biodegraded anaerobically by denitrification, iron reduction, and other microbial processes. Higher redox conditions are usually in favor of LNAPL biodegradation.
Dense non-aqueous phase liquids (DNAPLs), including but not limited to trichloroethene (“TCE”), are another type of contaminant found in groundwater and the like. Biologically catalyzed reductive dehalogenation may be a reducing process that reduces DNAPL to their final products. Reductive dehalogenation may occur under lower redox conditions, perhaps where acetogenesis, sulfidogenesis, methanogenesis and the like are dominant.
DNAPL (TCE and PCE, as but two examples) may be a major concern in groundwater contamination. These contaminants may transport rapidly down the vadose zone and end up in the groundwater. DNAPL tend to accumulate in bedrock, sediments or the like because of its high density and low water solubility. DNAPL may act as a source of groundwater contamination and may be recalcitrant to conventional remedial technologies. Reductive dehalogenation may be the most favorable bioremediation method for DNAPL clean-up in groundwater. As in LNAPL degradation, N nutrients may be a factor in shortage. However, conventional nitrogen amendments may have a very low efficiency for DNAPL degradation, possibly due to the high solubility of these amendments and the low solubility of DNAPL or for other reasons. This incompatibility may warrant a nitrogen source with relative DNAPL-affinity and time-releasing characteristics.
Enhanced bioremediation may overcome factors that may limit the rates of conventional pollutant biodegradation. Pollutant biodegradation may involve using enzymatic capabilities of indigenous microbes and perhaps modifying environmental factors such as oxygen, nitrogen, phosphorus, sulfur and electron acceptors concentration, as but a few examples. Nitrogenous (“N”) nutrients, such as ammonium nitrate, ammonium sulfate, urea, ammonium chloride, sodium nitrate, and the like have been studied and may have been shown under various conditions to stimulate microbial activities and degradation rates in soil and groundwater systems. Ammonium (NH4+), as may be a preferred N nutrient released by these source compounds, may be readily consumed by aerobic microbes for amino acid formation and other metabolisms. Nitrate (NO3−) may be a preferred N nutrient, as well as an electron acceptor, for anaerobic microbes to degrade hydrocarbons via denitrification.
Some nitrogen amendments may be highly soluble in water and large amounts of N nutrients may be released in short periods of time. Highly soluble N nutrients may not be available to groundwater microbes of low populations. In addition, NO3− may be lost due to denitrification and chemical decomposition. Frequent reapplications of these quick-releasing nitrogen fertilizers could be necessary to maintain the satisfactory biodegradation of contaminants, which could drive up the operational cost.
A slow-releasing N fertilizer should have one or more chemical or perhaps metabolic pathways and should be relatively insoluble in water. Urea may be considered as a slow-releasing N fertilizer since it may undergo hydrolysis before ammonium can be released. However, urea may be highly water-soluble and may even be subject to leaching through soil and dilution in groundwater. There may be slow-releasing N fertilizers, such as sulfur coated or polyolefin coated urea and the like, that may be relatively insoluble and may release N much more slowly than urea does. Yet, they may be energy intensive to produce, possibly making them an undesirable alternative due the high cost.
As such, highly soluble nitrogen compounds may be less bioavailable for microorganisms that are responsible for reductive dehalogenation, possibly resulting in expensive and low efficiency biodegradation. Although the role of nitrogen in biodegradation of LNAPL may be well recognized, and it may be equally critical in the bioremediation of DNAPL compounds.
DNAPL, such as the chlorinated solvent TCE, is a group of common contaminants in soil and groundwater. DNAPL transport rapidly down the vadose zone into the groundwater, and accumulate in bedrock or sediments due to their high mass density and low water solubility. DNAPL is a group of groundwater contamination that is recalcitrant to conventional remedial technologies. Under anaerobic conditions, such as in oxygen-depleted groundwater, TCE can be reductively dechlorinated by pure or mixed bacterial populations to less chlorinated ethenes and eventually to ethane (Holliger et al, 1993; Krumholz et al., 1996; Sharma and McCarty, 1996; Maymo-Gateil et al., 1997). Reductive dechlorination has been widely applied as an effective technique in cleaning up chlorinated solvents. This technology resolves the difficulty of inaccessibility to contaminants, as in other mechanical and physical remedies. Biodechlorination of chlorinated ethenes have been studied under various anaerobic conditions (nitrate reducing, sulfate reducing, iron reducing, and methanogenic processes) conditions (Bagley and Gossett 1990; Boopathy and Peters 2001; Bouwer and McCartey 1983; DeBruin et al. 1992; Flierman et al. 1988; Freedman and Gossett 1989; Hardman 1991; Hoelen and Reinhard 2004; Krone et al. 1989; Ndon et al. 2000). In some studies, dechlorination has been reported to cease at cis-1,2-dichlorethene (cis-DCE) and vinyl chloride (VC) in the presence of sulfate (Bagley and Gossett 1990; Boopathy and Peters 2001; Ndon et al. 2000). Complete dechlorination of TCE to ethene has been reported under methanogenic conditions (Bouwer and McCartey 1983; De Bruin et al. 1992). In other laboratory and field studies, dechlorination of PCE and TCE was observed occurring under or associated with sulfate reducing conditions (Bagley and Gossett, 1990; DiStefano et al., 1991; Pavlostathis and Zhuang, 1993; Maymó-Gatell et al., 1999; Ndon, et al., 2000; Drzyzga et al., 2002; Hoelen and Reinhard, 2004).
LNAPL, such as diesel and motor oil, are usually co-existing with DNAPL like TCE, although not necessarily in the same groundwater zone. In the site under study, free and soluble phases of LNAPL and DNAPL have formed a “four phase” system in the groundwater. Since the favorable degradation conditions for LNAPL are either in the presence of oxygen or other “higher-redox” electron acceptors, such as nitrate, the redox conditions sustaining reductive dehalogenation of DNAPL are not supportive to LNAPL degradation.
Fuel hydrocarbons are a group of co-contaminants frequently co-existing with chlorinated ethenes. Under proper conditions, capable microbes utilize fuel hydrocarbons as the carbon source for their metabolisms, converting them into shorter-chained intermediates and/or final products of carbon dioxide. When oxygen is depleted, as in most groundwater systems, nitrate reduction has been reported to be the most favorable pathway for hydrocarbon degradation (Al-Bashir et al. 1990; Durant et al. 1995; Leduc et al. 1992; Mihelcic and Luthy 1988). Typically, biodegradation of hydrocarbons depletes both oxygen and nitrate, leading to sulfate-reducing conditions (Hoelen and Reinhard 2004). Some studies have reported efficient biodegradation under sulfate-reducing conditions (Canfield et al. 1993; Coates et al. 1997; Reeburgh 1983). Consumption of the fuel hydrocarbons by sulfate reducers can channel protons/electrons to dehalogenating bacteria (e.g., dechlorinating bacteria), and, at least in the case of degradation of TCE, reductive dechlorination may be completed without accumulating cis-DCE and VC.
Further shortcomings of conventional technologies relative to bioremediation include the absence of methods that efficiently address the problem of co-contamination, i.e., the case where groundwater is contaminated with LNAPL and DNAPL, perhaps in different zones. At least one embodiment of the inventive technology provides a method whereby the contaminated groundwater is measured relative to concentrations (molar ratio, population per volume, as but two examples) of certain substances (living and non-living things, such as nitrogen, phosphorus, electron acceptor and/or bacteria, as but a few examples), and such measurements can be used to determine whether an amendment (e.g., an addition of a certain substance, whether living or non-living) should be added to enhance degradation of both LNAPL and DNAPL contaminants.